Influence of chlorination and the distribution system on mutagens in a potable water supply

A growing number of studies have detected mutagens in public water supplies. The widely accepted hypothesis that mutagenic substances are potential carcinogens therefore demands that these substances be characterized, isolated, and identified so that any potential adverse health effects can eventually be assessed. Previous studies have shown an association of water chlorination with the production of direct-acting mutagens. In the central Illinois public water supply described in this report, mutagens dependent on mammalian metabolism (promutagens) were found in addition to chlorination-related, direct-acting mutagens. Both kinds of mutagen were recovered by adsorption on polyurethane foam and quantitated by the Ames Salmonella/microsome reversion assay. Assay of the water from the groundwater source before treatment, following treatment, and after passage through the distribution system showed that the promutagens first appeared in the distribution system and that the direct-acting activity increased somewhat within it. The utility that supplies the water alternates disinfection monthly during the summer from chloramine to chlorination beyond breakpoint. Based on a year of weekly monitoring, it was found that chloramine disinfection produced water with more promutagenic activity than direct-acting mutagenicity and that chlorination beyond breakpoint reversed this order. Detailed study of the time of appearance of mutagens and chlorine residuals at one sampling tap showed patterns consistent with the formation of direct-acting mutagens by reaction of the free chlorine residual with substances in the water; these substances possibly were contributed by materials in the distribution system. Particulate matter collected from hydrant flush water at dead ends in the distribution system were found to harbor high amounts of two known animal carcinogens, benzo(a)pyrene and benz(a)anthracene, in addition to unidentified materials that contributed approximately as much mutagenicity as these two substances. These high levels of mutagens were not found in tap water extracts, nor could these carcinogens be identified in the tap water; they were exclusively associated with filterable particles in the hydrant flush samples. The origins of the identified and unidentified mutagens are currently unknown, but may include the leaching of materials from within the distribution system, reactions of such leached substances with the chlorine residual, or production by microorganisms known to reside in this distribution system that are associated with the dead ends where the highest levels of mutagens were found.U.S. Department of the InteriorU.S. Geological SurveyOpe